Reconstructing HoloceneHydroclimate from the

Sediments of OmbrotrophicPeatlands

Jonathan E. NicholsNASA Postdoctoral Program Fellow (NPP)

Goddard Institute for Space Studies

Implications ofHydroclimatic

change

Boston Globe/AP Photo

http://www.earth.columbia.edu/

Why Peatlands?• Extremely sensitive to hydrologic change

– Only input is precipitation• Common features of recently glaciated,

moist regions• High acidity and anoxia preserve fossil

molecules well (among other things)• Cover 3% of Earth’s surface but contain

30% of soil carbon

Two Purposes• Develop more quantitative

proxies for hydroclimatic &carbon cycle parameters

• Apply new proxies to develophypotheses about mechanismsof climate change

New Peatland Proxies1. Sphagnum/Vascular Ratio (SVR)

2. Hydrogen Isotopes ofPrecipitation (δDP)

3. Evaporation Remainder (ƒ)

n-Alkanes as Biomarkers• Sphagnum and vascular

plants have differentaverage n-alkanedistributions

• We can take advantage ofthis difference to measurechanges in hydrology

• A ratio of C23 to C29 n-alkane in peat samplesshows the relativeproductivity of eachgroup

Sphagnum

vascular plants

Sphagnum/Vascular Ratio (SVR)

Wet conditions:Sphagnum prospersMore C23, High SVR

Dry conditions:Sphagnum dries out and

vascular plants aremore productive

More C29, Low SVR

A two-part mixing model translates the C23:C29 ratio in a peat sampleinto a Sphagnum to vascular plant productivity ratio (SVR)

C23:C29 n-alkane ratio

Sphagnum

/Vascula

r R

atio (

SV

R)

Similar Changes in Distant Peatlands

Age, Cal. YBP

H - Isotopes and H - Isotopes and “δ”“δ” Notation Notation

D =

D/H (sample)

D/H (standard)

– 1( ) 1000VSMOW

1. Temperature(seasonality)

2. Moisture source3. Secondary evaporation

Rain Falls on the Bog andpercolates to theacrotelm.

Vascular plants use theacrotelmic water whichis not enriched byevaporation

While Sphagnum useswater at the surface

Which is enriched byevaporation

acrotelm

catotelm

Hydrogen Isotopes and Peatland Hydrology

Isotope Ratio Change Schematic

Rayleigh Evaporation Model:

ln f =Da Ds

k + *

We traceprecipitation δDand evaporationback fromsedimentarylipids

Climate Questions1. Mid-Holocene abrupt

climate shifts2. North Atlantic region:

hydroclimate changeforcings? Mechanisms?

Mid-Holocene Transition

• Global changes in hydroclimate at ~5.5ka• Manifests as abrupt shift toward dry

conditions in eastern North America– Contributed to the Hemlock Decline (abrupt

ecological change)

• Drought from modern era as an analogue:– “1960s Drought” 1962–1965

5.5ka Paleohydrologic RecordsAND

1960s Drought Anomalies

Irwin

Smith

Bog

The Great Heath

Both locations experience drought…

…but by different mechanisms

SUMMER DEFICIT WINTER/SPRING DEFICIT

Mean 1962-1965 Anomaly

H HHigh High δδDD

Low Low δδDD

850mb Wind Vectors, May-Oct.

Summer Mechanism:Subtropical High Position

Sea Level Pressure, Nov. - April

Mean 1962-1965 Anomaly

Carbon• Northern Peatlands: 3% of

land area but 30% of soilcarbon

• 5–10% of atmosphericmethane load

• Methane flux is stronglydependent on hydrology

• Symbiotic methanotrophsprovide δ13C depleted CO2

Wetter conditions --> moremethane reaches surface

More methane at surface --> lowerδ13C of sphagnum biomarkers

Summary• New Peatland Hydrologic Proxies

– SVR – total hydrologic balance– δD of C29 n-alkane – δD of precipitation– ƒ – evaporation remainder

• Mechanisms for North Atlantic Climate Change– Subtropical High Position– NAO-like mode of variability

• Future work will provide mechanistic understandingof hydrology/methane feedback

Thank You

New GISS/LDEO FamilyNew GISS/LDEO Family: Dorothy : Dorothy Peteet Peteet andandSanpisa SritrairatSanpisa Sritrairat

PhD AdvisorPhD Advisor: Yongsong Huang: Yongsong HuangCommitteeCommittee: Tim Herbert, Jack Mustard, Jim Russell,: Tim Herbert, Jack Mustard, Jim Russell,

Bob BoothBob BoothCollaboratorsCollaborators: Steve Jackson, Bob Booth, Elise: Steve Jackson, Bob Booth, Elise

PendallPendall, Ray Bradley, Jon , Ray Bradley, Jon PilcherPilcherIn the labIn the lab: Marcelo : Marcelo AlexandreAlexandre, Rafael , Rafael TarozoTarozo,,

Jonathan Wang, Jonathan Wang, Mana Mana TangTangIn the fieldIn the field: Nicole Nichols, Baird : Nicole Nichols, Baird LangenbrunnerLangenbrunner,,

Emily Emily PohlmanPohlman, Jess Tierney, Marcelo, Jess Tierney, MarceloAlexandreAlexandre,, Jonathan Wang, Jonathan Wang, Mana Mana Tang, Li Tang, Li GaoGao

In the office: Caitlin In the office: Caitlin ChazenChazen, Jaime Toney, Laura, Jaime Toney, LauraCleavelandCleaveland, Billy , Billy DD’’AndreaAndrea, , Juzhi HouJuzhi Hou